Management of Hyponatremia
Hyponatremia management depends critically on symptom severity and volume status, with correction rates never exceeding 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1
Initial Assessment
Determine symptom severity immediately as this dictates urgency of treatment 1:
- Severe symptoms (seizures, coma, altered mental status, respiratory distress): Medical emergency requiring immediate hypertonic saline 1, 2
- Mild symptoms (nausea, vomiting, headache, weakness): Less urgent correction 2, 3
- Asymptomatic: Conservative management based on underlying cause 2
Assess volume status through physical examination 1:
- Hypovolemic signs: Orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
- Euvolemic: No edema, normal blood pressure, moist mucous membranes 1
- Hypervolemic signs: Peripheral edema, ascites, jugular venous distention 1
Obtain essential laboratory tests 1:
- Serum and urine osmolality
- Urine sodium concentration
- Urine electrolytes
- Serum uric acid
- Assessment of thyroid and adrenal function 1
Treatment Based on Symptom Severity
Severe Symptomatic Hyponatremia (Emergency)
Administer 3% hypertonic saline immediately with target correction of 6 mmol/L over 6 hours or until severe symptoms resolve 1, 2, 3:
- Initial bolus approach: 100 mL of 3% saline over 10 minutes, can repeat up to 3 times at 10-minute intervals 1
- Monitor serum sodium every 2 hours during initial correction 1
- Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2, 4
Asymptomatic or Mildly Symptomatic Hyponatremia
Treatment is based on volume status 1, 3:
Treatment Based on Volume Status
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion 1, 3:
- Urine sodium <30 mmol/L predicts good response to saline infusion (positive predictive value 71-100%) 1
- Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
- Correction rate: 4-8 mmol/L per day, maximum 8 mmol/L in 24 hours 1
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment 1, 2, 3:
- If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
- For resistant cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate as needed) 1, 5
- Alternative options: urea, demeclocycline, lithium, or loop diuretics 1
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L 1, 2, 3:
- Discontinue diuretics temporarily if sodium <125 mmol/L 1
- For cirrhotic patients: Consider albumin infusion alongside fluid restriction 1
- Avoid hypertonic saline unless life-threatening symptoms present, as it worsens ascites and edema 1
- Tolvaptan may be considered for persistent severe hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to higher risk of gastrointestinal bleeding (10% vs 2% placebo) 1, 5
Critical Correction Rate Guidelines
Standard correction rates 1, 4:
- Average risk patients: 4-8 mmol/L per day, maximum 10-12 mmol/L in 24 hours 1
- High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 2
Calculate sodium deficit using formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1
Special Considerations
Neurosurgical Patients
Distinguish between SIADH and cerebral salt wasting (CSW) as treatments differ fundamentally 1:
- CSW treatment: Volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1
- For severe CSW symptoms: 3% hypertonic saline plus fludrocortisone in ICU 1
- Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1
- Consider fludrocortisone (0.1-0.2 mg daily) or hydrocortisone to prevent natriuresis 1
Cirrhotic Patients
Hyponatremia in cirrhosis increases risk of complications 1:
- Spontaneous bacterial peritonitis (OR 3.40) 1
- Hepatorenal syndrome (OR 3.45) 1
- Hepatic encephalopathy (OR 2.36) 1
Sodium restriction (not fluid restriction) results in weight loss as fluid passively follows sodium 1
Management of Overcorrection
If sodium correction exceeds 8 mmol/L in 24 hours 1:
- Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
- Consider administering desmopressin to slow or reverse the rapid rise in serum sodium 1, 6
- Monitor closely for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1
Common Pitfalls to Avoid
Critical errors that worsen outcomes 1:
- Overly rapid correction exceeding 8 mmol/L in 24 hours leads to osmotic demyelination syndrome 1, 2, 6
- Using fluid restriction in cerebral salt wasting worsens outcomes 1
- Inadequate monitoring during active correction 1
- Failing to recognize and treat the underlying cause 1
- Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
- Ignoring mild hyponatremia (130-135 mmol/L) as it increases fall risk (21% vs 5%) and mortality (60-fold increase with sodium <130 mmol/L) 1, 2
Monitoring Requirements
Frequency of sodium monitoring 1: